The present invention relates to the installation of a flangeless, non-piercing fasteners into a workpiece, such as, for example, a sheet metal panel.
Typically, fasteners are installed into a panel by piercing the panel with the fastener and plastically deforming the fastener and panel together. The assignee of the present invention has numerous patents to pierce type fasteners, methods for installing such fasteners, die buttons relating to such installation, heads for installing such fasteners, etc. Although pierce type fasteners are very effective in a wide variety of applications, there are some applications that do not benefit from their use. Another method of installing fasteners is by welding the fastener to the panel, a so-called weld nut. This method also poses problems in certain applications.
One example of a xe2x80x9cnon-pierce,xe2x80x9d non-weld type installation is in a pan that is to retain a liquid. A specific example of such a xe2x80x9cnon-pierce,xe2x80x9d non-weld application is the mounting of an air conditioner compressor to the condensation pan of an air conditioner. If the pan is pierced by a pierce type fastener, the pan has to be sealed at the pierce point. This can be done, for example, by using special fluid tight fasteners, separate sealing materials, coatings, etc. However, the use of these alternative methods can be relatively expensive and add to the overall cost of the assembly. With weld nuts the same problem occurs because the weld nut must be placed in a pre-pierced hole for welding. Weld nuts have further disadvantages as well. They require a longer cycle time than either pierce or non-pierce fasteners, there is spatter from the weld, heat from the weld can adversely effect the base metal and increase the potential for cracking, they are expensive and have toxicity problems when applied to galvanized materials.
Another xe2x80x9cnon-piercexe2x80x9d and non-weld type installation is in pre-painted or coated panels. With pre-painted or coated panels, the piercing operation can adversely effect the paint or coating, particularly at the pierce point. The piercing of the panel creates exposed metal that can rust and must be treated to prevent rusting. By using a xe2x80x9cnon-piercingxe2x80x9d fastener, there is no exposed metal and the integrity of the paint or coating is not disturbed. Weld nuts cannot be welded to painted materials rendering them fairly useless unless the surface area is cleared of paint. This would be an expensive, time consuming process which would still have exposed surface area.
The present invention provides a solution to the above disadvantages that occur when using pierce type fasteners in the situations outlined. The present invention discloses a non-pierce type fastener, a die button, a method for attaching the non-pierce fastener to a workpiece, and an assembly having the non-pierce fastener and workpiece to provide a strong assembly without the disadvantages of piercing.
The fastener of the present invention has an attachment portion for connecting the fastener to another member, such as a panel. The attachment portion is disclosed as a threaded shaft that can receive a standard nut. A connecting head extends from the attachment portion. The connecting head is defined by a drive shoulder which is adapted to be engaged by a plunger of an installation head. The drive shoulder extends outwardly from and generally perpendicular to the attachment portion. A barrel extends at an angle from the drive shoulder and is adapted to engage and interlock with the workpiece. The barrel has a sidewalk extending from the drive shoulder which ends in a surface engaging end face. The surface engaging end face engages the panel and deforms the panel about the barrel to lock the fastener to the panel. The sidewalk has an outer surface and an inner surface and the connecting head includes a base surface opposite the drive Surface. The inner surface and the base Surface define an inner recess area or pocket that is adapted to receive a portion of the panel upon installation of the fastener.
In one embodiment of the invention, the fastener includes a retention groove located between the base surface and along the inner Surface of the sidewalk. Preferably, the retention groove is located at the juncture of the base surface and the sidewalk. The retention groove provides additional retention between the panel and the fastener when the panel is wrapped around the barrel of the fastener.
In the preferred embodiment, the barrel is flared outwardly with respect to the longitudinal centerline of the fastener in the form of a truncated cone. Preferably, it is flared at a minimum of 20xc2x0 from vertical.
The barrel of the preferred embodiment has a flat wide face for contacting the panel surface. This provides a large surface area to engage the panel and not pierce the panel. This surface area also allows the barrel face and the panel to slightly slide relative to one another so that the panel is not sheared by installation forces. The outer and inner edges of the barrel are rounded to provide a smooth edge surface to prevent piercing or shearing of the panel during installation.
The preferred fastener also includes anti-rotation means to prevent the fastener from rotating with respect to the workpiece when installed. Preferably, the anti-rotation means are located along the inner surface of the barrel. In one embodiment, the fastener anti-rotation means are protrusions positioned about the barrel. In another embodiment, the fastener anti-rotation means are indents positioned about the barrel. The fastener could also have indents and protrusions.
The method of attaching the fastener to a workpiece includes the steps of positioning the workpiece between the die button and the fastener and driving the fastener into the workpiece to initially engage the barrel of the fastener against the workpiece and deform the workpiece into the recessed portion of a die button. This places an area of the workpiece in tension. It should be appreciated that the barrel is not deformed during the installation process, unlike pierce type fasteners. The fastener is driven further into the workpiece to thin the workpiece adjacent the barrel. The workpiece is trapped between the barrel outer edge and a transition surface in the die button. Between these two points the workpiece is in tension and stretched.
As the fastener is driven further into the workpiece, the forces on the same portion of the workpiece are reversed from tensile forces to compressive forces which squeezes the workpiece adjacent the transition surface and pushes the workpiece against the barrel. This reversal is caused by the workpiece being bottomed into the die cavity and the plunger deforming the top surface of the workpiece. As the workpiece bottoms into the die button, the barrel edge is still being driven into the panel which causes the workpiece metal to be pushed around the edge of the barrel. Simultaneously, the plunger is deforming the workpiece in the direction of the die bottom causing metal to move in the direction of the bottom and forcing the metal between the edge and the plunger to flow into the recess between the plunger and the outer surface of the sidewalk. The transition surface of the die button directs the flowing metal into the recess and assists in packing it about the outer surface of the sidewalk. The bottom of the die button assists as well.
The installation process is completed by finally driving the fastener home to lock the fastener into the workpiece. The inner pocket of the barrel receives the workpiece as it is forced into the pocket when the fastener is finally driven into the workpiece. The workpiece can also be forced into the retention groove if provided to further lock the fastener to the workpiece. This wraps the workpiece around the edge and face of the barrel and into the retention groove. In tile preferred embodiment, the panel is thicker than the depth of the pocket to further assist in packing of metal into the pocket and if provided the groove.
The die button that is used has a top surface with a cavity formed into it. The cavity is defined by an inner wall surface and a bottom surface. The inner wall surface has a transition surface that is generally adjacent the recess between the outer surface and tile plunger of the fastener. The transition surface is located between the top surface of the die button and the bottom of the cavity. The transition surface allows the panel to be bent and drawn during the initial installation step and then compressed as the installation is completed. In the disclosed embodiment of the die button, the wall has a first sloping section that ends at the transition surface and a second sloping section that has a greater slope than the first. This second section terminates in a radiused corner which ends in a slightly inclined surface. The inclined surface ends in a rounded protrusion. The inclined surface is stepped and ends in the bottom surface of the cavity. The die button is also disclosed with a vent hole to prevent the workpiece from being locked in the die button, for example by hydraulics created during the installation process.
The resulting fastener and panel assembly provides an assembly with good pull-out characteristics and no pierced openings. The assembly includes the fastener having a connector for connecting the fastener to another member and the panel engaging head at one end of the connector with its barrel. The panel has the formed recess into which the fastener is locked. The recess is partially defined by a wall and non-pierced base. The wall has a formed recess having a shape generally complementary to the shape of the barrel and pocket so that the recess generally mates with the barrel and is locked around the barrel.
Other advantages and meritorious features of the present invention will become more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.